The invention relates to a semiconductor device comprising a source electrode, a drain electrode and a source bus. The invention also relates to a method of forming patterns of a source electrode, a drain electrode and a source bus.
In recent years, TFT (thin film transistor) devices have been commonly used in liquid crystal displays for, for example, notebook personal computers. A TFT is constructed by forming on a substrate, various kinds of films such as metal films and insulation films having various patterns. In order to form the pattern of each of such films, the material for each of the films is first deposited on the substrate. Then, the desired pattern corresponding to each of the films is defined in the deposited material by means of a lithography method. Accordingly, the more the number of the films to be patterned increases, the more the number of the patterning processes using lithography method increases, which may be resulted in the increase of the manufacturing cost.
In order to cope with this kind of problem, it is considered not to perform a method of etching a single film but to perform a method in which, firstly, a double layer is formed by layering two kinds of films, and next, the double layer is continuously etched. According to the latter method, the desired pattern is defined in these two kinds of films by performing only one patterning process.
However, in this method of etching the double layer, another one film must be etched compared with etching a single layer. Thus, a difference in level between an etched portion and a non-etched portion formed in the double layer (i.e., a depth of an etched portion) becomes deep comparing with the single layer. Therefore, if a further film is formed on the etched double layer so as to cover the difference in level of the double layer with the further film, the step coverage of that further film may become worse at the difference in level of the double layer, and as a result the characteristic of the film may be deteriorated. On the other hand, if two kinds of films consisting of the double layer are not continuously etched but separately etched, there is a problem that the manufacturing cost may increase.
In view of the above-described background, it is an objective of the invention to provide a semiconductor device and a method for forming patterns in which the manufacturing cost is reduced while the step coverage is improved.
In order to achieve the above-described objective, the invention provides a method of forming patterns. Said method is characterised by comprising a step of forming a first metal film on a substrate, a step of forming a second metal film on said first metal film and a step of forming patterns of a source electrode, a drain electrode and a source bus by patterning said second and first metal films, wherein said step of forming the patterns of the source electrode, the drain electrode and the source bus comprises a step of forming a resist coat on said second metal film and a first etching step of dry-etching said second and first metal films after said step of forming said resist coat.
In this method of forming patterns, after having formed the resist coat on the second metal film, not only the second metal film but also the first metal film that is formed below the second metal film could be etched. Therefore, when etching the second and first metal films, there is no need to form a specific resist coat for patterning the second metal film and another specific resist coat for patterning the first metal film. This may be resulted in a reduction of the manufacturing cost.
Besides, in this method of forming patterns, since those metal films are dry-etched, a difference in level between an etched portion and a non-etched portion is formed in the second and first metal films. In this case, even if another film is formed to cover the second and first metal films having that difference in level, a good step coverage of this another film can be obtained at the difference in level (as will be described in detail later).
In particular, in this method of forming patterns, said first metal film is preferably an ITO film mainly including ITO, the second metal film is preferably a molybdenum-chromium film mainly including a molybdenum material, and said first etching step is preferably a step of dry-etching said molybdenum-chromium film and said ITO film with a mixed gas of chlorine and oxygen. By dry-etching the molybdenum-chromium film and the ITO film with a mixed gas of chlorine and oxygen, edge portions of the molybdenum-chromium film and the ITO film could be formed in taper shape.
Besides, said method may comprise, instead of said first etching step, a second etching step of wet-etching said second metal film and then dry-etching said first metal film. Even if this second etching step is provided instead of the first etching step, the manufacturing cost reduction can be still achieved. In the second etching step, a difference in level between an etched portion and a non-etched portion is formed in the second and first metal films. However, a good step coverage at the difference in level can be obtained just as in the case of the first etching step (as will be described in detail later).
In addition, in this inventive method, said first metal film preferably has a thickness not greater than 500 angstrom. By keeping such thickness, a good step coverage can be achieved.
Furthermore, in this inventive method, said first metal film is preferably an ITO film mainly including ITO, the second metal film is preferably a molybdenum-chromium film mainly including a molybdenum material, and said second etching step is preferably a step of wet-etching said molybdenum-chromium film with a mixed etchant of phosphoric acid, nitric acid and water and subsequently dry-etching said ITO film with a gas mainly including chlorine. Through such wet-etching and subsequent dry-etching steps on the molybdenum-chromium film and the ITO film, the edge portions of the molybdenum-chromium film and the ITO film could be formed either substantially perpendicularly or in taper shape relative to the substrate.
Furthermore, said method comprises, instead of said first etching step, a third etching step of wet-etching said second and first metal films and then wet-etching said second metal film further. Even if that third etching step is used instead of the first etching step, the manufacturing cost reduction can be achieved. In the third etching step as well, a difference in level between a etched portion and a non-etched portion may be formed in the second and the first metal films. However, a good step coverage at the difference in level can be obtained. With the third etching step, said first metal film has a thickness not greater than 500 angstrom. By keeping such thickness, the good step coverage can be achieved.
Additionally, in said third etching step, said first metal film is preferably an ITO film mainly including ITO, the second metal film is preferably a molybdenum-chromium film mainly including a molybdenum material, and said third etching step is preferably a step of wet-etching said molybdenum-chromium film with a mixed etchant of phosphoric acid, nitric acid and water, subsequently wet-etching said ITO film with a hydrochloric acid etchant and further wet-etching said molybdenum-chromium film with a mixed etchant of phosphoric acid, nitric acid and water. Through such third etching step of the molybdenum-chromium film and the ITO film, the molybdenum-chromium film and the ITO film could be formed substantially perpendicularly relative to the substrate.
A semiconductor device according to the present invention is characterised by comprising a source electrode formed on a substrate, a source bus formed on said source electrode, a drain electrode that is formed on said substrate and comprises a first electrode and a second electrode formed on said first electrode, and further characterized in that an edge portion of said source electrode protrudes toward said drain electrode relative to an edge portion of said source bus and an edge portion of said first electrode of said drain electrode protrudes toward said source electrode relative to said second electrode.
By applying the above-mentioned method of forming patterns, the edge portion of the source electrode can protrude toward the drain electrode relative to the end of the source bus and the edge portion of the first electrode of the drain electrode can protrude toward the source electrode relative to the edge portion of the second electrode. Such structure means that, for example, in the case of forming an a-Si film that is to be connected to both electrodes of the source and drain electrodes, the a-Si film would be formed in such a way that a good ohmic contact is obtained between each of the source and drain electrodes and the a-Si film.
In the semiconductor device according to the present invention, each edge portion of said source electrode, said source bus, said first electrode and said second electrode may be formed into a surface either which is perpendicular to said substrate or which is inclined relative to said substrate. If using the first etching step according to the present invention, each edge portion of the source electrode, the source bus, the first electrode and the second electrode may be formed into a surface which is inclined relative to the substrate (i.e., taper shape), whereas if using the second or third etching step according to the present invention, each edge portion of the source electrode, the source bus, the first electrode and the second electrode may be formed into a surface which perpendicular to the substrate.